4 research outputs found
Photoregulating RNA Digestion Using Azobenzene Linked Dumbbell Antisense Oligodeoxynucleotides
Introduction of 4,4′-bisÂ(hydroxymethyl)-azobenzene
(azo)
to dumbbell hairpin oligonucleotides at the loop position was able
to reversibly control the stability of the whole hairpin structure
via UV or visible light irradiation. Here, we designed and synthesized
a series of azobenzene linked dumbbell antisense oligodeoxynucleotides
(asODNs) containing two terminal hairpins that are composed of an
asODN and a short inhibitory sense strand. Thermal melting studies
of these azobenzene linked dumbbell asODNs indicated that efficient <i>trans</i> to <i>cis</i> photoisomerization of azobenzene
moieties induced large difference in thermal stability (Δ<i>T</i><sub>m</sub> = 12.1–21.3 °C). In addition,
photomodulation of their RNA binding abilities and RNA digestion by
RNase H was investigated. The <i>trans</i>-azobenzene linked
asODNs with the optimized base pairs between asODN strands and inhibitory
sense strands could only bind few percentage of the target RNA, while
it was able to recover their binding to the target RNA and degrade
it by RNase H after light irradiation. Upon optimization, it is promising
to use these azobenzene linked asODNs for reversible spatial and temporal
regulation of antisense activities based on both steric binding and
RNA digestion by RNase H
Mirror-Image Thymidine Discriminates against Incorporation of Deoxyribonucleotide Triphosphate into DNA and Repairs Itself by DNA Polymerases
DNA
polymerases are known to recognize preferably d-nucleotides
over l-nucleotides during DNA synthesis. Here, we report
that several general DNA polymerases catalyze polymerization reactions
of nucleotides directed by the DNA template containing an l-thymidine (l-T). The results display that the 5′–3′
primer extension of natural nucleotides get to the end at chiral modification
site with Taq and Phanta Max DNA polymerases, but the primer extension
proceeds to the end of the template catalyzed by Deep Vent (exo<sup>–</sup>), Vent (exo<sup>–</sup>), and Therminator DNA
polymerases. Furthermore, templating l-nucleoside displays
a lag in the deoxyribonucleotide triphosphate (dNTP) incorporation
rates relative to natural template by kinetics analysis, and polymerase
chain reactions were inhibited with the DNA template containing two
or three consecutive l-Ts. Most interestingly, no single
base mutation or mismatch mixture corresponding to the location of l-T in the template was found, which is physiologically significant
because they provide a theoretical basis on the involvement of DNA
polymerase in the effective repair of l-T that may lead to
cytotoxicity
Role of Secondary Particle Formation in the Persistence of Silver Nanoparticles in Humic Acid Containing Water under Light Irradiation
The wide use of silver
nanoparticles (AgNPs) leads to the increasing
release of AgNPs into the environment. Dissolved organic matter (DOM)
is a key factor affecting the behaviors and fate of AgNPs in the aquatic
environment. However, the mechanisms for the DOM-mediated transformations
of AgNPs are still not fully understood. In this study, we investigated
the persistence of AgNPs in the aquatic environment in the presence
of different concentrations of humic acid (HA) over periods of time
up to 14 days. The Ag species were monitored and characterized by
absorption spectrometry, transmission electron microscopy (TEM), inductively
coupled plasma mass spectrometry (ICP-MS), and multicollector ICP-MS
(MC-ICP-MS). Results showed that the long-term persistence of AgNPs
in HA-containing water was determined by two critical concentrations
of HA. When the HA concentration exceeded a lower critical value,
AgNPs could be persistent in the solution, and a large number of AgNPs
were formed secondarily from the HA-induced reduction of the Ag<sup>+</sup> ions released from the primary AgNPs, causing a redistribution
of the particle size. With the HA concentration above a higher critical
value, AgNPs could persist in the solution without a significant change
in particle size. Notably, we used Ag isotope fractionation to investigate
the transformation mechanism of AgNPs. The natural isotopic analysis
by MC-ICP-MS revealed that the size redistribution of AgNPs caused
significant Ag isotope fractionation, which gave additional evidence
for the proposed mechanisms. This study provides new insights into
the environmental fate of engineered AgNPs and highlights the usefulness
of stable isotope fractionation in environmental nanotechnology
Antibody-Free Colorimetric Detection of Total Aflatoxins in Rice Based on a Simple Two-Step Chromogenic Reaction
The prevalently used immunoassays
for fast screening of aftatoxins
(AFs) usually cannot meet the requirement for simultaneous determination
of total AFs (aflatoxin B<sub>1</sub> + aflatoxin B<sub>2</sub> +
aflatoxin G<sub>1</sub> + aflatoxin G<sub>2</sub>) due to the deficiency
of highly group-specific antibodies. This paper describes a two-step
chromogenic reaction based method to quantitatively detect total AFs
in rice using colorimetric measurement without antibody. In the method,
colorless AFs transform into green-colored indophenol products through
the reaction with sodium hydroxide and 2,6-dibromoquinone-4-chloroimide
(DBQC) successively, allowing selectively determining total AFs up
to 3.9 μg/kg over other competitive mycotoxins under optimal
conditions by a UV–vis spectrophotometer. In addition, the
colorimetric measurement results of the rice samples agree well with
that of a standard HPLC method, demonstrating the good reliability
and applicability of the method. Uniquely, the method has potential
for on-site detection of total AFs in rice when using a nylon membrane-based
device